Sump pumps are required in all present and new construction that is below grade level. The sump pump prevents the build up of water around the foundation. This prevents the water pressure from building up and cracking the foundation or leaking into the basement and causing water damage. To prevent this damage, perforated drain tile is placed around the basement footing which allows the water to seep into the tile and gravity feed to a sump pit. The sump pit contains a pump that is used to discharge the water away from the foundation. In some construction, an additional sump pump may be provided to pump water from a washing machine into the main sanitary sewer system. Generally, sump pump pits are from 15 to 18 inches in diameter and from 24 to 36 inches deep. Anything smaller could cause the pump to run too often or not be able to handle a large volume of water from a downpour.
There are two types of sump pump, the older pedestal pump and the newer submersible pump. The pedestal pump has the motor above the water in the pit and a long shaft extending down into the pit to pump the water. Submersible pumps are waterproof and placed directly in the pit to pump the water. Submersible pumps are more commonly employed today because they are more efficient and allow the pit to be completely enclosed. In addition, since the pump is below the water level, they are quieter.
Two items are required to complete the installation of a sump pump. A check valve (one way valve) is installed into the pump vertical discharge line to prevent pumped water from flowing back into the sump when the pump shuts off. The second item required is the water level switch that makes the operation automatic. Switches come in several types, including floats; diaphragm pressure switches and tethered tilt switches. Almost all of these switches employ mechanical means to control the large sump pump motor current and are subject to contact failure.
It has become common to finish basements so that the space is useable as living areas. The sump pump is needed to keep the basement living area dry, but the operating noises of the pump are objectionable. The check valve is the greatest cause of noise, especially where the pump is submersible. Every time the automatic switch turns the pump off, the water flow is interrupted and the reverse flow causes the valve to slam shut with a loud thud. The sudden shut off of the valve causes the discharge pipe to violently vibrate and rattle the wooden plate of the house where it passes through. The effect of the check valve is similar to the noise generated when a water valve in the house is suddenly closed off. To eliminate or reduce the effect of water hammering, expansion air volumes are installed on water valves that close suddenly, i.e. solenoid valves on the washing machine and dishwasher. A similar solution could be applied to the sump pump check valve; however, there is little headroom for an expansion air volume since the discharge pipe exits the house near the basement ceiling. There are a few precautions that can help to reduce the hammering. A check valve located at the base of the pump instead of above the floor level may help. When the valve is located next to the pump, the mass of the sump pumps can help reduce vibration and the surrounding water will also reduce the sound. The discharge pipe should not be fastened to the wooden plate where it exits the house. Instead, the discharge pipe should pass freely though a larger diameter pipe that is fastened to the wooden plate. The space between the two pipes can then be filled with foam insulation or fiberglass loosely packed to close the gap. This allows the discharge pipe some freedom to vibrate with out rattling the house.